Overhoist limit switch



April 1967 J. BAKER ETAL OVERHOIST LIMIT SWITCH 4 Sheet-5heet 1 Filed Jan. 11, 1965 a 7 c e 7 H 2 O o l! L l C 1\ I. I ||v|| IIIE. W l 7 ml p IIIJIIIJ. |l IV llllllllll b ////M. QUV\ u 7 w O 2 2 r PVKIIIILQTI HI 2 5 L m H IIIIIJ n w rllL ll INVENTORS. JAME'S BAKER new 501/40 Cf/AEZES AlM/V saw Re MAT TORNEY.

April 1967 J. BAKER ETAL 3,315,045

OVERHOIST LIMIT SWITCH Filed Jan. 11, 1965 4 Sheets-Sheet 2 w i no INVENTORS. JAMES BAKE)? #4 50 50040 CHAEZES ALIA/V SCfi/U/Pl? ,i jv' E ATTORNEY.

April 18, 1967 Filed Jan. 11, 1965 J. BAKER ETAL OVERHOIST LIMIT SWITCH 4 Sheets-Sheet 5 INVENTORS. JAMES EA KER FRED EQULD awe; 4144 50/1/21? fi m TORNEY.

April 18, 1967 J. BAKER ETAL OVERHOIST LIMIT SWITCH 4 Sheets$heet 4 Filed Jan. ll, 1965 5 m w IF MELM M W 5 0 4 M 5 A M M 5 a W arm M c United States Patent Ofilice 3,315,045 OVERHOIST LiMlT SWITCH James Baker, Black Mountain, N.C., Fred Bould, Pittsburgh, Pa., and Charles Allan Schurr, Shaker Heights,

Ohio, assignors to Square D Company, Park Ridge, Ili.,

a corporation of Michigan Filed Jan. 11, 1965, Ser. No. 424,565 6 Claims. (Cl. 20047) This invention relates to an improvement in limit switches and, more particularly, to an improved limit switch for automatically discontinuing the energization of a motor when the mechanism driven by the motor moves beyond a predetermined limit of operation.

The improved limit switch is particularly suitable as an overhoist limit switch for a crane hoist. Electrically operated crane hoists are commonly provided with an overhoist limit switch for disconnecting the hoist drive motor from its source of power in the event the hook of the hoist is permitted to travel beyond a predetermined safe upper limit. Such limit switches are provided to insure that the hook or moving sheaves of the hoist will not, either upon operator error or failure of the motor controller, interfere with parts of the hoist and thereby strain the hoisting cable excessively and possibly cause damage to the hoist or mechanism, perhaps causing dropping of the load.

For this reason, it is desirable to provide a limit switch which will, upon movement of the hoist beyond a predetermined limit, automatically disconnect the drive motor from its source of energization regardless of the mode of operation in which the hoist controller has been set. It is also desirable that the limit switch, upon disconnection of the motor from its source, be adapted for reconnecting the motor in a circuit, such as the well-known dynamic braking circuit, which will aid the motor in coming quickly to rest.

Overhoist limit switches have long been used on hoists driven by electric motors. Many such switches are commonly equipped with a weight which biases the switch to its normal position and which is lifted by the hook or moving sheave upon hoisting thereof beyond a predetermined safe upper limit. The weight, when so lifted, permits a counter-weight to cause a snap-acting mechanism to operate the contacts of the limit switch with a positive and rapid movement.

The prior switches, however, have the disadvantage of being relatively difiicult to assemble. Also, they are, for the most part, exceedingly large and cumbersome for their current rating.

It is an object of the present invention to provide an improved limit switch which is compact and relatively easy to assemble.

Another object is to provide an improved limit switch having its principal operating components, including the operating arm and counter-weight, carried by a single continuous shaft supported only at its opposite ends by respective bearings.

A further object is to provide an improved limit switch having blowout coils and the respective cores thereof supported solely by the conductors forming the respective coils.

A further object is to provide an improved limit switch having a su port means fabricated of non-conducting material thereby to provide a compact structure yet having adequate insulation between the current conducting parts.

A further object is to provide an improved limit switch which, even in the event of failure of the spring which normally cooperates with a snap-acting means to operate the switch contacts, remains operative.

A more detailed object is to provide an overhoist limit 3,315,045 Patented Apr. 18, 1967 switch comprising support means, a continuous operating shaft oscillatably supported by the support means for oscillation about the longitudinal axis of the shaft, movable contacts mounted on the shaft for movement therewith, stationary contacts adapted to be engaged by the movable contacts, operating means journalled on the shaft and rotatably movable relative thereto, and snap acting means operatively interposed between said operating means and said shaft, the operating means being operative to cause said snap-acting means to rotate said shaft with a snap action when the operating means is rotated relative to the shaft.

Various other objects and advantages will become apparent from the following description, wherein reference is made to the drawings of a preferred embodiment of the invention and in which:

FIG. 1 is a perspective view of an overhoist limit switch embodying the present invention;

FIG. 2 is a top plan view of a limit switch embodying the principles of the present invention, the switch cover and the arc.chute in the left portion of the switch being omitted for clearness in illustration.

FIG. 3 is a cross sectional view taken on the line 3-3 of FIG. 2;

FIG. 4 is a cross sectional view of FIG. 2;

FIG. 5 is a cross sectional View taken on the line 5-5 of FIG. 2; and,

FIG. 6 is an elementary wiring diagram illustrative of an application of the limit switch to the control of a direct current motor.

Referring to FIGS. 1 through 5, an overhoist limit switch in accordance with this invention comprises a support means having a mounting frame 10, a base 11, and a bearing support 12. The base 11 and bearing support 12 are secured to the mounting frame 10, as by screw or bolt fasteners 14. The base 11 preferably is fabricated, as by molding, of non-conducting insulating material, such as molded phenolic, and has an end wall 11a and support projections 11]) and 11c molded integrally with, and disposed normally of, the base.

An operating shaft 15 is journalled at its opposite ends in respective bearings 16 and 17, the bearing 16 being carried by the bearing support 12 and the bearing 17 being carried by the end wall 11a of the base 11.

Operating means, comprising a weight arm 18 and an operating arm 20 having a camming member 20a, are journalled on the operating shaft 15 by a pair of bearings 21 for rotational movement relative to the shaft 15. The operating arm 20 is fixedly secured to the weight arm 18 for rotation therewith relative to the shaft 15 by fastener means such as bolts 22. For economy of manufacture and ease of assembly, the bearings 16, 17 and 21 are preferably identical.

Snap acting means comprising a rocker arm. 24, a pair of identical latch members 25 and 26, and a torsion spring 27 having projecting ends 27a and 27b, cooperate with the operating arm 20 to oscillate the shaft 15 when the operattaken on the line 44 for rotation therewith, as a roll pin 24d. In addition, the rocker arm 24, as best shown in FIG. 4, has latching surfaces 240 and 24b which cooperate, respectively, with complementary shoulders 25a and 26a of the latch members 25 and 26, respectively. The rocker arm 24 also has a projecting arm 24c positioned intermediate the ends 27a and 27b of the spring 27.

Movable contact means, such as the contact assemblies 28 and 30, are fixedly secured by fastener means, such as one or more bolt and nut combinations 31 (only one of which is shown), to an insulator 34 carried by the shaft and rotatable therewith. The movable contact assemblies 28 and 30 are identical; therefore, for purposes of explanation, only the movable contact assembly 28 will be described in detail.

As best illustrated in FIG. 5, the movable contact assembly 28 comprises a contact bracket 35, a pair of identical contact arms 36 and 37, to each of which a contact tip 38 and an arcing tip 39 are secured by suitable fastener means 40, a contact spring 41, and a pair of identical contact retainers 42. Each of the contact arms 36 and 37 has an end portion 44 having a rounded surface which is received in a complementary portion 45 of the bracket 35. The arms 36 and 37 are retained in position in the assembly 28 by the retainers 42 which are secured to the bracket by fastening means such as a bolt and nut 46. Shoulders 47 on the arms 36 and 37, respectively, cooperate with bent-over end portions 48 of the retainers 42 to prevent the arms 36 and 37 from being withdrawn upwardly out of the assembly 28 and to maintain the cooperative relationship of the portions 44 and of the arms 36 and 37 and the bracket 35, respectively. The arms 36 and 37 also have suitable holes adapted to receive means such as roll pins 51 which cooperate with slots 52 and 54 in the retainers 42 to further insure that the arms will be retained in proper position in the assembly 28.

Thus, there is provided in each of the assemblies 28 and 30 a pair of identical contact arms 36 and 37 which are movable independently of each other, against the bias of the spring 41, relative to the bracket 35. As will be readily observable to those skilled in the art, the economical use of identical components in the contact assemblies 28 and 30, and the absence of pinned fasteners between the arms 36 and 37 and the bracket 35, provide an assembly which is compact and can be readily assembled and disassembled.

Each of the contact arms 36 and 37 also has a suitably threaded bore 55 adapted to receive a bolt for securing electrical conductors to the respective arms. The respective electrical conductors leading from the arms 36 and 37 of the movable contact assembly 28 are mechanically and electrically joined by a fastener 56 which is secured to an insulating non-conducting mounting board 57. The respective conductors from the arms 36 and 37 of the movable contact assembly 30 are connected together by a fastener 58 which is secured to an insulating mounting board 59, similar to the mounting board 57. The mounting boards 57 and 59 are carried by the base 11 in recesses or slots provided in the end wall 11a and in the supporting projections 11b and 11c. In the preferred embodiment of this device, the boards 57 and 59 are cemented in place.

Stationary contact assemblies 60, 61, 62, and 63 are provided to cooperate with the movable contact assemblies 28 and 30. The contact assemblies 60 and 61 are secured to the mounting board 57 and the contact assemblies 62 and 63 are secured to the mounting board 59 by suitable fasteners 64, respectively.

Because the mounting boards 57 and 59 are identical and because the stationary contact assemblies 60 through 63 are identical with each other, only the contact assembly 62, best illustrated in FIG. 5, will be described in detail. For each stationary contact assembly, such as the assembly 62, there is provided a stationary contact bracket 65 having a projecting arc transferring member 66, a contact tip 67 secured to the bracket 65 by a suitable fastener 68, and a blowout coil 70. A flux-conducting core 72, electrically insulated from the blowout coil 70 by an insulator 74, is positioned in the coil 70. One end 70a of the blowout coil 70 is retained in electrical conducting relationship in a recess of the bracket 65 as by welding or soldering. The other end 70b of the blowout coil 70 is formed into a loop and is fastened by a fastener 71 to the mounting board 59. The fasteners 71 serve as electrical wiring terminals for the stationary contact assemblies 60 through 63.

An arc chute 75 is provided for the stationary contacts 61 and 63 and their associated movable contact assembly 30. A second arc chute identical to the chute 75 is provided for the stationary contacts 60 and 62 and their associated movable contact assembly 28. The two arc chutes are identical and only the arc chute 75 will be described in detail.

The are chute 75 comprises a pair of identical body portions 76 held together in cooperative relationship with each other by suitable fasteners 77, such as binding post and screws. Flux-conducting blowout ears 78, two on each body portion 76, or a total of four for each arc chute, are carried, exteriorly of the assembled body portions, in suitable cavities or recesses provided in the body portions 76 and are secured in place by flux-conducting screw fasteners 80. The fasteners 80 are preferably flat head screws having their head portions received in countersunk holes on the interior of the assembled arc chute so that the heads of the screws are flush with the interior surface of the body portions 76 of the arc chute.

Each of the body portions 76 of the arc chute has a recessed portion 81 defining a shoulder 81a shaped to complement the profile of the arc transferring member 66.

When the arc chute is asembled, the shoulders 81a provide a means which cooperate with the arc transferring members 66 for supporting and properly positioning the arc chute in the switch. The are chutes 75 may thus be removed from the switch to facilitate inspection of the contacts merely by lifting them out without the necessity of disassembling or removing any fastening means whatsoever.

The screw fasteners 80 are so positioned that, when the arc chutes are properly positioned in the switch, the heads of the screw fasteners will be in flux-conducting abutting relationship with the ends of the cores 72 of the blowout coi'ls 78, as shown in FIG, 2.

The operation of the switch is as follows:

Assuming the switch mechanism to be in its normal position as shown in the drawings, counterclockwise rotation of the weight arm 18 and the operating arm 20 which is secured thereto causes the camming member 20a of the operating arm 20 to contact the projecting end 27a of the torsion spring 27. Because the bias of the spring 27 tends to urge its ends 27a and 27b together, the end 27b follows the member 20a and comes into abutting relation with the projecting arms 240 of the rocker arm 24. The rocker arm 24 and shaft 15, together with the movable contact assemblies 28 and 30, are thus far prevented from rotation by the interference of the latching surface 24a with the shoulder 25a of the latch member 25.

Continued counterclockwise rotation of the weight arm 18 and the operating arm 20 causes the camming member 20a to force the spring end 27a away from the arm 240. In this manner the spring force acting through its end 27b tends to urge the arm 24c and consequently, the shaft 15 in a counterclockwise direction. Upon further counterclockwise movement, the camming member 20a strikes an edge 25b of the latch member 25 and the shoulder 25a is moved out of interference with the latching surface 24a. Thereupon the spring 27 causes the shaft 15 and movable contact assemblies 28 and 30 to rotate with a snap action in the counterclockwise direction so as to bring the contact tips 38 into engagement with their respective stationary contact assemblies 62 and 63.

The switch is maintained in the tripped position by engagement of the shoulder 26a of the latching member 26 with the latching surface 24b of the rocker arm 24 until a subsequent clockwise rotation of the weight arm 18 and operating arm 20 causes the switch to be reset to its The operation of the mechanism to similar to that described during the normal position. reset the switch is tripping operation.

The blow-out coils 70 and are chutes 75, previously described, assist in extinguishing the electrical are which occurs upon opening of the switch contacts under load. The principles of operation of a blowout coil and are chute are well known to those skilled in the electrical art and require no further explanation herein.

Electrical conductors 82, which are provided for connection to respective terminals at the fasteners 56 and 58 for the movable contact assemblies 28 and 30 and to terminals at the fasteners 71 for the stationary contacts, are brought out of the switch through openings 84 in the end wall 11a of the base 11.

A cover 86, preferably molded of an insulating nonconducting material and having an integrally molded arc barrier 87, is provided with clasps 88 for securing the cover to the mounting frame 10.

Because the sole driving means for the operating shaft and movable contacts of the switch, as thus far described, is the spring 27 and, because it is desirable that the switch contact be operative even in the event of breakage of the torsion spring 27 or welding together of the contacts, means are provided to insure positive operation of the operating shaft 15 for both the tripping and resetting operations. Referring to FIGS. 3 and 4, the operating arm 20 is provided with a pair of pins 20b which cooperate with shoulders 24:: in the rocker arm 24 so as to provide a lost motion mechanical connection. With the switch in either the normal or tripped position, when the weight arm 18 and operating arm 20 are rotated to cause the switch to operate to its other position, if the spring 27 fails to drive the operating shaft 15, the pins 20b will, after the appropriate latch member is moved out of interference with its respective latching surface 24b, engage the shoulders 24c and force the shaft 15 and movable contacts to their other position.

The diagram of FIGURE 6 illustrates a well-known manner of connecting an overhoist limit switch in the power circuit of a direct current motor. In this diagram only the connections essential to explain the operation of the device are shown, the conventional control apparatus for varying the speed and direction of rotation of the motor being omitted. It is to be further understood that the application of the limit switch herein described is not limited to use with the direct current motor shOWn, its use with other types of motors in circuits utilizing both alternating and direct current being apparent from the illustrative exarrmle.

In the circuit shown in FIGURE 6, a motor 90 having a series field winding 91 and an armature winding 92 provided with terminals 92a and 92b is energized from a source of direct current represented by respective positive and negative terminals 93 and 94. The positive terminal 93 of the source is electrically connected to stationary contacts 67:: and 67b through the field winding 91 and, also, to a stationary contact 67a. A fourth stationary contact 67a is electrically connected to the negative source terminal 94. One terminal 92a of the armature winding 92 is electrically connected to a pair of movable contacts 38a and 38b, the other terminal 92b of the armature winding is electrically connected to a pair of movable contacts 38c and 38d.

In the normal operating position, as shown in FIGURE 6, the movable contacts 38b and 38d are engaged with their respective stationary contacts 67b and 67a thereby permitting current to flow from the positive source terminal 93 through the motor field winding 91, the contacts 67b and 38b, thence through the armature winding 92, the contacts 38d and 67d, to the negative source terminal 94. Upon the motor 90 reaching its limit of operation and upon consequent operation of the limit switch to its tripped position, as previously described, the contacts 38b and 67b and the contacts 38d and 67d are caused to open and the movable contacts 38a and 38c are engaged with their respective stationary contacts 67a and 67c. Thereupon, the motor is removed from its source of power and a closed loop dynamic braking circuit is established from the motor armature terminal 92a through the contacts 38a and 67a, the field winding 91, and the contacts 670 and 380 to the armature terminal 921;. The full line arrows in FIGURE 6 show the direction of current flow under normal conditions, whereas the arrows in dotted lines show the direction of current flow for braking when the switch is in its tripped position.

Having thus described our invention we claim:

1. An overhoist limit switch comprising:

support means;

stationary contacts carried by the support means;

an operating shaft oscillatably supported at its opposite end portions in respective bearings carried directly by said support means, thereby permitting oscillation of said shaft about its longitudinal axis;

movable contacts fixedly mounted on said shaft for movement therewith, into and out of engagement with the stationary contacts;

operating means, including a weight arm, journalled solely on said shaft between said bearings and rotatably movable relative to said shaft, in opposite direction, to preselected positions, respectively; and

snap acting means operatively interposed between said operating means and said shaft;

said operating means being operative to cause said snap acting means to oscillate said shaft with a snap action in one direction when said operating means is moved in one of said directions to one of said positions, and to oscillate said shaft with a. snap action in the other direction when said operating means is moved in the oposite direction to another of said positions.

2. An overhoist limit wherein:

the operating means are journalled on the shaft on additional bearings, and said bearings which support said operating shaft and the additional bearings for said operating means are identical with each other.

3. An overhoist limit switch comprising:

support means;

an operating shaft directly supported at its opposite end portions in respective bearings carried by said support means, thereby permitting oscillation of said shaft between a first and a second position;

movable contact means fixedly mounted on said shaft for movement therewith between said first and second positions;

a first set of stationary contacts adapted to be engaged by said movable contact means when said shaft is in said first position;

a second set of stationary contacts adapted to be engaged by said movable contact means when said shaft is in said second position;

snap-acting means; and

operating means, including a weight arm, journalled solely on said shaft between said bearings and oscillatably movable relative to said shaft;

said operating means cooperating with said snap-acting means when the operating means is oscillated about said shaft to predetermined positions, respectively, to oscillate said shaft between said first and second positions.

4. An overhoist limit switch according to claim 3 wherein:

the operating means are journall-ed on the shaft on additional bearings, and said bearings which support said operating shaft and the additional bearings for said operating means are identical with each other.

5. An overhoist limit switch comprising:

a support;

an operating shaft mounted directly on the support for switch according to claim 1 oscillation about the longitudinal axis of said shaft; stationary contacts on the support;

movable contacts fixedly mounted on the shaft for movement therewith into and out of contact, respectively, with the stationary contacts upon oscillation of the shaft in opposite directions, respectively, to predetermined positions;

a Weight arm journalled on, and supported solely by, the shaft for rotational movement relative to the shaft, and adapted for movement in opposite directions by a device to be controlled;

an operating arm fixedly secured to said weight arm for movement therewith upon movement of the Weight arm in opposite directions, respectively, to predetermined positions;

snap-acting means operatively drivingly interconnecting the operating arm and shaft for oscillation of the shaft with a snap action to one of its said predetermined positions upon movement of said weight arm to one of its predetermined positions, and for oscillation of the shaft with a snap action to the other of its said predetermined positions upon movement of said weight arm to the other of its predetermined positions.

6. An .overhoist limit switch according to claim 3 wherein said operating means additionally includes an operating arm fixedly secured to said weight arm for oscillatory movement therewith about said shaft, and camrning means on said operating arm; and wherein said snap-acting means comprises a pair of latch members pivotally secured to said support means and having respective latching shoulders, a rocker arm fixedly secured to said operating shaft for oscillation therewith and having a pair of latching surfaces, one of said latching surfaces engaging one of said latching shoulders in said first position of said shaft, and the other of said latching surfaces engaging the other of said latching shoulders in said second position of said shaft, thereby to maintain said rocker arm and said shaft in said first and second positions, selectively, and a torsion spring resiliently connecting said operating arm and said rocker arm and tending to bring said arms into rotational alignment, said camming means alternately engaging said latch members upon movement of said operating means between said predetermined positions thereby to alternately release the latching shoulders of said latch members from engagement with their associated latching surfaces of said rocker arm so as to permit said spring to move said rocker arm and said operating shaft with a snap-action between said first and second positions.

References Cited by the Examiner UNITED STATES PATENTS BERNARD A. GILHEANY, Primary Examiner.

T. MACBLAIN, H. E. SPRINGSBORN,

Assistant Examiners. 

1. AN OVERHOIST LIMIT SWITCH COMPRISING: SUPPORT MEANS; STATIONARY CONTACTS CARRIED BY THE SUPPORT MENAS; AN OPERATING SHAFT OSCILLATABLY SUPPORTED AT ITS OPPOSITE END PORTIONS IN RESPECTIVE BEARINGS CARRIED DIRECTLY BY SAID SUPPORT MEANS, THEREBY PERMITTING OSCILLATION OF SAID SHAFT ABOUT ITS LONGITUDINAL AXIS; MOVABLE CONTACTS FIXEDLY MOUNTED ON SAID SHAFT FOR MOVEMENT THEREWITH, INTO AND OUT OF ENGAGEMENT WITH THE STATIONARY CONTACTS; OPERATING MEANS, INCLUDING A WEIGHT ARM, JOURNALLED SOLELY ON SAID SHAFT BETWEEN SAID BEARINGS AND ROTATABLY MOVABLE RELATIVE TO SAID SHAFT, IN OPPOSITE DIRECTION, TO PRESELECTED POSITIONS, RESPECTIVELY; AND SNAP ACTING MEANS OPERATIVELY INTERPOSED BETWEEN SAID OPERATING MEANS AND SAID SHAFT; SAID OPERATING MEANS BEING OPERATIVE TO CAUSE SAID SNAP ACTING MEANS TO OSCILLATE SAID SHAFT WITH A SNAP ACTION IN ONE DIRECTION WHEN SAID OPERATING MEANS IS MOVED IN ONE OF SAID DIRECTIONS TO ONE OF SAID POSITIONS, AND TO OSCILLATE SAID SHAFT WITH A SNAP ACTION IN THE OTHER DIRECTION WHEN SAID OPERATING MEANS IS MOVED IN THE OPPOSITE DIRECTION TO ANOTHER OF SAID POSITIONS. 